1. Field of the Invention
The disclosure relates generally to a drain regulator for a NOR flash memory, and more particularly to a drain regulator providing a constant output voltage for efficiently programming the selected cell of a NOR flash memory.
2. Description of the Related Art
Memory devices are typically provided as internal, semiconductor, integrated circuits in computers and other electronic devices. There are many different types of memory, including random-access memory, read only memory, dynamic random access memory, synchronous dynamic random access memory, and flash memory.
Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Common uses for flash memory include personal computers, personal digital assistants, digital cameras, and cellular telephones. Program code and system data such as a basic input/output system are typically stored in flash memory devices for use in personal computer systems.
As electronic systems and software become more complex, they require additional memory capacity. However, as flash memory device sizes increase, the time and power required to program the memory also increases. This can decrease system performance.
NOR-type flash memory devices typically use a Channel Hot Electron (CHE) method of programming CHE involves a high current on the bit line and through the cell, between the drain and source, which is being programmed. The bit line current also consists of the sum of the parasitic current from all other cells on the same bit line, which are intended to be in an “OFF” state and yet still leak some current. The current leakage increases overall current draw from the bit line charge pump and also increases the voltage drop in the bit line path due to the additional IR drop. This results in lower programming efficiency.
For the reasons stated above, there is a need in the art for more efficient programming of a flash memory transistor.